In molding synthetic resin by an injection molder or extruder, the molder is washed when type of resin it molds is to be changed, with the resin that will next be molded to remove the residues of the preceding resin. However, washing a molder by such a method takes a long time, needs large quantities of wash resin, and cannot completely wash complex structures within the molder, with the result that the molded articles of the subsequent resin may be discolored, and their qualities, such astransparency, degraded.
It is very important for molding synthetic resin to reduce the quantity of wash resin and the washing time for a molder, when color or type of resin it molds is to be changed, in order to maintain or improve productivity.
In order to solve the above problems, detergents of thermoplastic resin compositions, incorporated with a detergent component, have been developed, and are used to clean a molder when type of resin it molds is changed.
For example, Japanese Laid-open Patent Application No. 124046/1993 discloses a resin composition for washing molders that mold thermoplastic resins, which comprises (a) a thermoplastic resin incorporated with (b) 1 to 20 wt. % of a sulfonic acid-based surfactant, (c) 1 to 30 wt. % of an inorganic salt or metallic hydroxide having water of crystallization, starting to be dehydrated at 100.degree. C. or higher [e.g., Al(OH).sub.3 ], (d) 1 to 20 wt. % of an inorganic filler. Japanese Patent Publication No. 78557/1994 discloses a resin composition for washing molders, which comprises (A) a thermoplastic resin incorporated with (B) factice, (C) slip additive and (D) non-ionic surfactant.
However, the methods for producing these compositions involve problems. For example, it is disclosed that the method for producing the former composition mixes a molten thermoplastic resin with one or more essential components and auxiliary components, also molten, by a kneader such as monoaxial or biaxial extruder. As a result, each particle of the composition contains the detergent component deep inside. For the latter composition, it is disclosed that the thermoplastic resin A is mixed with the other components A to D by a tumbler or high-speed mixer and the mixture is kneaded by an extruder. These detergents proposed so far have been produced by the methods, which fall into the category of kneading.
As described above, these detergents contain a detergent component dispersed inside the detergent particles. As a result, it takes a long time for the detergent component to diffuse to the particle surface during the washing step, even though large quantities of the expensive component being incorporated into the resin. It covers only part of the particle surface, even when it diffuses to the surface. Use of such a detergent needs a long washing time and a large quantity of the resin to be molded subsequently. Therefore, there is increased need for a detergent that can avoid these problems.